1. Field of the Invention
The invention concerns a photosensor for a transmitted-light method for detecting the direction of movement of the intensity maxima and intensity minima in an intensity profile, with a transparent substrate, two first semiconductor components assigned to the substrate, and at least three contacts.
2. Description of the Prior Art
In the field of photoelectric detection of visual radiation, photosensors that operate by a wide variety of principles are used, e.g., as photoresistors, photodiodes, phototransistors, or the like. A common feature of all of these designs is that the visual radiation is detected by the incident-light method. Typical applications for these types of photosensors are, e.g., light barriers or monitoring and security systems.
Another very specific area of application of photoelectric detection is optical interferometers. A typical example and one which is often used for technical length measurements is the Michelson interferometer, in which a beam splitter splits a light beam into two split beams, which then follow different paths and, after being reflected back to the beam splitter plate, are recombined at the plate. In accordance with the state of the art, two signals with a mutual phase shift of 90° are photoelectrically derived from the differential structure produced at the interferometer exit to detect the direction of movement of the measuring mirror. As in the case of all of the other photoelectric applications mentioned above, the detection of the radiation also occurs in incident light.
By contrast, when an optical standing wave forms, the two beams that produce the interference propagate in opposite directions. For this reason, the technical utilization and photoelectric evaluation of the result of the interference of an optical standing wave can be carried out only in transmitted light.
DE 33 00 369 and U.S. Pat. No. 4,443,107 describe designs for a standing-wave interferometer. In line with the requirements on interferometers for the automatic detection of the direction of movement of the measuring mirror, two photosensors are provided in each case, which generate two signals with a mutual phase shift of 90° for detecting the direction of movement of the measuring mirror. The photosensors are applied to a glass substrate, whose thickness must be finished with a precision of a few nanometers by the methods of optical precision finishing to maintain the 90° phase shift as precisely as possible. This requires the application of considerable technological resources, which is associated with high costs.
DE 36 12 221 describes placing a piezoelectrically active component between the two photosensors and making the distance between the sensors adjustable. Although this solution significantly reduces the expenditure of technological resources, it is still necessary, e.g., in the event of temperature changes, to detect any changes in the distance between the sensors and to adjust the distance.